Abstract

Limited entry technique is often employed to achieve uniform flow distribution between perforation clusters during hydraulic fracturing treatment. However, the proppant distribution between clusters will not necessarily be uniform, even if the slurry distribution is uniform. As the average slurry velocity reduces from one cluster to another, this leads to proppant settling and higher particle concentration in the lower portion of the wellbore. Also, the slurry makes a sharp turn to enter a perforation and the higher proppant density causes some particles to miss the perforation. These two physical effects are primarily responsible for the non-uniform proppant distribution between the clusters. In view of these observations, the purpose of this study is to investigate the degree of uniformity of proppant placement based on a recently developed proppant-wellbore dynamics model. A field scale case consisting of 13 perforation clusters is considered. Three perforation designs are compared: the original design with 3 perforations phased 120°, a case in which the orientation of each individual perforation shot is optimized, and a case in which phasing is optimized with the constraint that all perforations have the same orientation. The goal of the optimization procedure is to achieve more uniform proppant distribution. Results are presented in the context of uncertainty of perforation diameter and phasing. Finally, the effect of stress shadow from the previous stage on the variability of proppant placement is investigated. It is found that the optimal perforation phasing leads to a significantly more uniform proppant distribution between perforations and that the effect of stress shadow does not significantly alter the results as soon as sufficiently strong perforation friction is used. Uncertainty of perforation phasing and diameter introduces a certain level of variation to the results, but this level is noticeably smaller compared to the improvement achieved by using the optimal perforation orientation.